Field of the Invention
Embodiments of the present invention relates to the art of a reinforcement structure for a vehicle bumper that is deformed to absorb collision energy of a vehicle colliding with an obstacle.
Discussion of the Related Art
JP-A-2001-322517 describes a bumper beam comprising a base member attached to the front or rear of an automobile, and a reinforcement member having high compressive stiffness attached to the base member. The bumper beam taught by JP-A-2001-322517 can absorb low-speed impact without permanent deformation, and the base member and the reinforcement member are designed to be deformed by relatively high speed impact to absorb collision energy.
JP-A-2004-203066 describes a vehicle bumper assembly in which an upper wall and a lower wall of a bumper reinforce is prevented from being damaged to reduce displacement of the bumper reinforce. To this end, according to the teachings of JP-A-2004-203066, a reinforcement member having a hollow space is fitted onto a front wall of the bumper reinforce as a rectangular pipe in such a manner to cover the upper and lower walls.
JP-A-H04-143014 describes a reinforcement steel tube for vehicle body. According to the teachings of JP-A-H04-143014 a short cylindrical cover member is fitted onto a width center of the reinforcement steel tube so that the steel tube is bent at both ends of the cylindrical cover to prevent a local deformation toward a vehicle interior.
Bending strength of the bumper at width center can be enhanced by the reinforcement members taught by the above-mentioned prior art documents and hence the kinetic energy generated by an impact applied to the width center of the bumper can be dissipated to supporting members at width ends of the bumper. That is, larger energy can be absorbed by the bumper thus reinforced.
An absorption capacity of the bumper of this kind is governed by a product of a deformation and a reaction of the bumper. In order to enhance the absorption capacity of the bumper, therefore, it is preferable to enhance deformability of the bumper in addition to enhance bending strength. For example, deformability of the bumper may be enhanced by arranging a plurality of reinforcement members on the bumper to increase a number of bend points at both width ends of each reinforcement member where the bumper is fractured by the collision impact. However, once the bumper is fractured at some of the bend point(s), reaction of the bumper is no longer established and hence the bumper may not be fractured at the other bend points as intended. For this reason, absorption capacity of the bumper may not be enhanced as desired.